This invention relates to a scroll compressor in which the capacity of the compressor is reduced when the temperature of the refrigerant becomes high. High temperature is indicative of a low charge, loss of charge or reverse rotation, and the reduction of the capacity provides a protective function.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a pair of scroll members each having a base and a spiral wrap extending from the base are placed facing each other. The spiral wraps of the two scroll members interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and the spiral wraps define decreasing volume compression chambers as the one scroll member orbits relative to the other.
Scroll compressors raise many design challenges. One challenge relates to operation of the scroll compressor when the charge of refrigerant becomes low. In such so-called xe2x80x9closs of chargexe2x80x9d operation, the temperature of the refrigerant becomes undesirably high. The temperature also can be high during reverse rotation, low suction pressure operation or other abnormal conditions. Damage can result to the components of the scroll compressor from the high temperatures.
Thus, it would be desirable to have a mechanism for protecting the scroll compressor in a loss of charge situation.
Reduced capacity systems are known for scroll compressors. However, the reduced capacity systems have generally been used to achieve a reduced capacity when a variable outside of the compressor indicates a need for a reduced charge. Thus, if a control decides that the cooling capacity, as an example, is low, then the capacity of the compressor may be reduced.
Similar problems are encountered during low suction pressure operation, reverse running operation, or other conditions which could result in an elevated temperature.
In a disclosed embodiment of this invention, an internal condition in the scroll compressor is sensed, and the capacity of the compressor is reduced in response to that sensed condition. Preferably the orbit radius of the orbiting scroll is reduced upon the condition being sensed.
In several embodiments, a bi-metal or shape memory alloy metal component does not actuate the orbit reduction until a predetermined temperature is reached. If the predetermined temperature is reached, then a component is actuated which reduces the orbit radius. As one example, a pin is fixed in the orbiting scroll, and extends upwardly into a chamber in the non-orbiting scroll. A cap which has a ramped inner surface is biased away from the pin, and received in the chamber. Discharge pressure refrigerant is selectively tapped to the reverse side of the cap. A bi-metal valve prevents flow of the discharge pressure to the chamber under normal operating conditions. However, if the temperature becomes high, then the bi-metal valve allows flow of discharge pressure to the chamber, and the cap is biased downwardly such that it prevents the full orbiting movement of the pin. When the pin""s orbiting movement is restricted, the orbit movement of the orbiting scroll is also restricted.
In a second embodiment, the pin is offset relative to the axis of the chamber. The cap includes an eccentric passage which selectively receives the pin. Normally, the cap is biased away from the pin. However, when the discharge pressure is directed into the chamber, the cap is biased downwardly to contact the pin. At this time, the orbiting radius of the orbiting scroll is reduced.
In another embodiment, a suction pressure is tapped to one side of a pin-piston. A spring also biases the pin-piston upwardly into a groove in the rear face of the orbiting scroll. The pin-piston is movable within the back pressure chamber of the scroll. The back pressure chamber is typically at an intermediate compressed pressure. Thus, the intermediate pressure is normally sufficiently high such that the pin-piston is biased downwardly and is not moved into the groove.
In a low charge, low suction pressure, and reverse running situations, the suction pressure approaches the intermediate compressed pressure. In these conditions, the spring will bias the pin-piston upwardly into the groove. Thus, the orbiting radius of the orbiting scroll is reduced.
A similar embodiment, rather than utilizing suction pressure versus intermediate pressure, a bi-metal element is utilized which selectively biases the pin upwardly when the refrigerant reaches an elevated temperature.
In another embodiment of this invention, a pin-piston is received in a groove in a base of the orbiting scroll. A first torsion spring twists the pin in a first direction. A second shape memory alloy tends to bias the pin in a second direction. Under normal xe2x80x9crelaxedxe2x80x9d conditions, the torsion spring overcomes the force from the shape memory alloy, and the pin is biased to a position at which it does not affect the orbit of the orbiting scroll. However, upon an elevated temperature being encountered in the refrigerant, the shape memory alloy increases its force on the pin, and the pin is moved to a position at which it reduces the orbiting radius of the orbiting scroll.
In another embodiment, a fluid-filled bellows forces a shim outwardly against a pin received in the orbiting scroll. The fluid filled bellows is normally retracted under normal operating temperatures. However, upon the occurrence of an elevated temperature, the bellows expands forcing the shim against the orbiting pin. This would then reduce the orbiting radius of the orbiting scroll.
In yet another embodiment, a shape memory alloy actuator selectively forces a pin radially outwardly to contact the Oldham coupling. Thus, upon the occurrence of an elevated temperature, the pin is forced outwardly to contact the Oldham coupling. This limits the reciprocating movement of the Oldham coupling, and consequently limits the orbit radius of the orbiting scroll.
In general, the present invention discloses a number of embodiments wherein the orbit radius of the orbiting scroll is limited by elements which are actuated upon a sensed condition within the orbiting scroll.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.